The point of my colorful title and judgmental post is that in the example, passing :e for the declared parameters as declared is a pointless operation at best, and in most practical situations it is also an erroneous operation.
The language designers have (arguably for the good) chosen to complain about various actual argument mismatches vs. formal parameters. If I tried to call foo with only one argument I'd get an error about missing arguments (or more generally, arity). Similarly, in this case, calling foo with :e should complain about superfluous arguments, all assuming that foo is declared as intended. Without an :as option on the destructuring, there is nothing that can be done to meaningfully process a keyword to the function named :e. I am proposing the language should do better in this case. If not now, perhaps 2.0. On Sat, Aug 22, 2015 at 9:06 PM, Colin Yates <colin.ya...@gmail.com> wrote: > Hi Dave, it _isn't_ an Illegal argument though :-), your destructuring > is simply ignoring that parameter. > > However, I get the pain and solutions might be (in order of 'heavyness'): > - http://blog.fogus.me/2009/12/21/clojures-pre-and-post/ > - https://github.com/Prismatic/schema > - http://typedclojure.org/ > > HTH > > Dave Tenny writes: > > > I sure wish Clojure would generate "IllegalArgumentException" in the > > following sample case: > > > > (defn foo [a b & {:keys [c d]}] 1) > > (foo 1 2 :e 5) ; blithely ignores :e 5 > > > > I understand that Clojure's destructuring things are very nice, and more > > powerful than Common Lisp's, and I like > > that when I need it. > > > > However I can't tell you how many times I've been bitten by this. Some > > simple typo or other other parameter name error on keyword arguments > > with untended and way-too-long-to-debug consequences. > > > > In my mind, on this subject, Common Lisp lambda lists got this right and > > Clojure gets a poor grade. > > Something about being doomed to repeat history. In Common Lisp, if you > > really wanted to allow other (arbitrary) keywords you'd > > just use &allow-other-keys. > > > > Maybe clojure should only allow the above case to go un-complained-about > if > > :as was specified for the map. > > > > If there's some automatic enforcement I'm missing that comes with 'defn' > > please let me know, I'm still learning the language. > > > > I've thought more that once about making a common lisp DEFUN statement > that > > maps to DEFN but implements > > lambda list semantics (including 'supplied-p' parameters). I've just > been > > too lazy to do it. > > > > It would also likely perform poorly after injecting the additional > > checks/rearrangements into the function on top of what Clojure has > already > > done, > > so I suppose it would have to be taken a step further so that it didn't > > generate DEFN expressions at all but was implemented at DEFN's level as > > a seperately named form. > > > > Tips welcome. Just thinking aloud. > > > > - Dave > > -- > Sent with my mu4e > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > --- > You received this message because you are subscribed to a topic in the > Google Groups "Clojure" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/clojure/3-CevvzQg1s/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > clojure+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
